The processing and utilization of food generally involves five functions accomplished by the digestive tract. They include motility, secretory, digestive absorptive and elimination functions. Processing of food begins in the oral cavity where food is mechanically broken down by mastication, lubricated with saliva, and enzymatically processed by amylase present in the saliva. Processing continues in the stomach where food is liquefied by gastric juices and enzymes secreted by the cells lining the stomach to produce chyme. Chyme enters the small intestine via the pyloric sphincter for further processing by bile salts produced by the liver and digestive enzymes produced by the pancreas. The small intestine absorbs most components from chyme through its walls, and the large intestine subsequently processes components that are not absorbed by the small intestine. Finally, the large intestine propels waste products into the colon, where they remain, usually for a day or two, until the feces are expelled by a bowel movement.
Sometimes, a person takes an abnormally long time to process and digest food, or a person may process food too quickly. This abnormal gastrointestinal function can be contributed to a disorder that affects the digestive tract, whether it be a disorder in the stomach or a disorder beyond the stomach. Commonly, a disorder occurs in the stomach that causes food to be emptied from the stomach into the small intestine too quickly or after too long of a time. Stomach emptying disorders (“dysmotility”) can be diagnosed by measuring the rate at which a meal empties from the stomach and enters the small intestine (the “gastric emptying rate”). When the rate is accelerated, ingested food is prematurely dumped from the stomach to the small intestine, giving rise to the condition termed “rapid emptying” or otherwise known as the dumping syndrome. Conversely, when the rate is decelerated, the movement of ingested food from the stomach to the small intestine is delayed, giving rise to the condition termed “delayed emptying” otherwise known as gastroparesis.
Two known tests for measuring gastric emptying rates are quantitative scintigraphy tests and gastric emptying breath tests (“GEBT”). In scintigraphy testing, a patient ingests a meal including at least one edible food, a component of which has been radiolabeled. The gamma emission from the radiolabel is measured by a scintillation camera as the labeled food is emptied from the stomach. Scintigraphy measurements of gastric emptying are direct, since the camera directly measures the gamma emissions arising from the radiolabeled meal remaining in the stomach. In breath testing, a patient ingests a meal that includes a non-radioactive marker or label, e.g., carbon-13 (13C), a stable, non-radioactive isotopic form of carbon. As the non-radioactive labeled edible food is processed by the digestive tract, a labeled component, e.g., 13CO2, is produced which can be detected in the patient's breath. In contrast to scintigraphy, measurement of gastric emptying using breath testing is indirect. Results for both types of testing are interpreted as either positive (abnormal) or negative (normal) for either gastroparesis or for accelerated emptying. Test results are therefore viewed from a dichotomous point of view.